1. Field of the Invention
The present invention relates to a contactor device for a circuit breaker, which comprises a stationary contactor composed of a stationary contact and a stationary conductor secured with the stationary contact and constituting an electricity path extending from an external terminal to the stationary contact, and a movable contactor composed of a movable contact movable to detachably touch the stationary contact, and a movable conductor secured with the movable contact and constituting an electricity path extending from the movable contact to another external terminal.
2. Prior Art
FIG. 17 shows the contactor device of a conventional circuit breaker, which includes a stationary conductor 4 shaped as a U-shaped plate and having two mutually parallel portions 4a and 4b. A stationary contact 5 is secured to the outside surface of the portion 4a. A movable contact 6, which is moved into and out of touch with the stationary contact 5, is secured to a movable conductor 7 provided in parallel with the two mutually parallel portions 4a and 4b of the stationary conductor. The stationary conductor 4 and the stationary contact 5 constitute a stationary contactor. The movable conductor 7 and the movable contact 6 constitute a movable contactor. The stationary contactor and the movable contactor constitute the contactor device of the circuit breaker.
When the circuit breaker with the contactor device thus constituted cuts off a heavy current such as an overcurrent at a relatively high voltage, an arc generated between the stationary contact 5 and the movable contact 6 at the time of the cut-off of the heavy current needs to be quickly driven in between arc extinguishing plates 14a in an arc extinguishing chamber 14 and cooled by the arc extinguishing plates to heighten the arc voltage to the voltage of a power supply. For that reason, the relative portions of the contacts 5 and 6 and the arc extinguishing plates 14a, the number and dimensions of the plates and so on are determined so that the arc generated between the contacts 5 and 6 is quickly driven in between the plates and cooled by the plates to heighten the arc voltage to the voltage of the power supply while the arc is moved and lengthened in the order of a, b and c as shown in FIG. 18.
However, if the property of recovery of insulation between the stationary contact 5 and the movable contact 6 has only a small margin for the circuit voltage or is insufficient therefor, an arc is generated again between the contacts 5 and 6 at the time of appearance of a recovery voltage therebetween after the current cut-off action of the circuit breaker or the former arc continues to exist without a clear no-current period present before the generation of the latter arc, so that the arc repeatedly takes sequential states shown by a, b and c in FIG. 18. In that case, it is impossible to cut off the current finally. In order to prevent such a phenomenon to surely cut off the current, the gap between the contacts 5 and 6 needs to be enlarged as shown by a one-dot chain line in FIG. 18. As a result, however, the circuit breaker becomes larger and more expensive if it is for a relatively high voltage circuit, resulting in drawback.